Cheng Wang’s research while affiliated with Beijing Institute of Technology and other places

The accidents caused by explosions often result in a variety of destructive threats. Protection techniques designed for a single destructive factor are difficult to resist the multiple threats that may exist in the explosion, so it is urgent to have a multi‐effective protection function of the protection technology. Within the scope of this research, a new modified polyurea with the addition of halloysite nanoparticle fillers was designed and produced. The influence of different ratios of halloysite on the thermal properties, mechanochemical properties, shock wave attenuation properties, and penetration resistance of the material was investigated. The experimental results show that the addition of halloysite to polyurea materials can significantly improve their thermal stability, thermal insulation and flame retardancy, and also enhance their mechanical properties under quasi‐static and dynamic loading. In addition, the halloysite particles can enhance the shock wave attenuation of polyurea materials, and the attenuation effect can be about 20% when the content of halloysite is 3%. Moreover, the addition of halloysite improves the penetration resistance of the polyurea material, increasing the ballistic limiting velocity of halloysite‐modified polyurea to 1.24 times that of the pure polyurea material. Highlights The halloysite‐modified polyurea material was designed. The effect of halloysite particles on polyurea materials was investigated. The materials were evaluated for thermal, mechanical, and protective properties.

A hydrogen/air flame propagation and the development of tu lip ­ shaped flame in 2D tubes of different aspect ratios with both closed ends and in a half-open rectangular channel were studied using high resolution direct numerical simulations o f the fully compressible Navier - Stokes equations coupled with a detailed chemistry. Flame propagation in a 3D rectangular channel was studied using large eddy simulations and compared with the results of direct numerical simula­ tions of flame propagation in a 2D rectangular channel with the same aspect ratio. It is shown that the interaction of the rarefaction wave generated by the flame at the deceleration stage with the "positive" flow of unburned gas generated by the flame at the previous accel­ erating stage leads to a significant decrease of the velocity of the unburned gas flow in the near field zone ahead of the flame front. As a result, the thickness of the boundary layer in the near-field zone ahead of the flame increases significantly, and the profile of the axial velocity of the unburned gas in the near-field zone ahead of the flame front takes the form of a tulip or an inverted tulip, which leads to corresponding changes in the velocities of different parts of the flame front, the flame front inversion, and the formation of a tulip-shaped flame.

In this study, experiments on underwater explosions near a wall at water depths of 200–500 m were conducted in a pressure tank using 5 g aluminized explosives with varying aluminum powder content (0%–15%). The shock wave load, bubble contraction and collapse load, jet load, and impulse on the wall were measured. A numerical model simulating underwater explosions at depths ranging from 200 to 2000 m was developed, and the experimental data were used to validate the model's accuracy and the reliability of the simulation results. The effects of water depth and aluminum powder content on explosion load characteristics near the wall and on jet evolution were analyzed. The results showed that for the shock wave load, as water depth increased, the energy released by the afterburning reaction of the aluminum powder also increased. However, the dissipation of the shock wave energy exceeded the increase in peak overpressure, resulting in a net decrease in the shock wave load. The increase in aluminum powder content extended the positive pressure duration of the shock wave, thereby increasing the impulse of the shock wave. For the jet load, when the jet was in the same phase of bubble pulsation, an increase in water depth primarily increased the peak overpressure of the jet load, while an increase in aluminum powder content mainly extended the jet duration, thereby increasing both the impulse and the damage ability of the jet load.

An optimal ignition criterion must be selected for the numerical prediction of the ignition parameters for mechanical spark ignition of near-limit methane–air fuel mixtures based on fuel mixture equivalency ratio; wherein, the vast majority of ignition criteria can be used for stoichiometric fuel mixtures. However, the viability of each criterion must be individually determined for near-limit fuel mixtures. This study developed a high-resolution algorithm that can be used to model the mechanical spark ignition and combustion of methane–air fuel mixtures of varying equivalence ratios. Three ignition criteria, Van’t Hoff, reaction heat release rate, and −OH concentration, were evaluated at varying equivalence ratios based on their respective distributions at varying times. The widely used Van’t Hoff criterion cannot be used to predict near-limit fuel mixtures due to a high required ignition temperature and low rates of combustion. −OH concentration criterion is significantly affected by the rate of combustion and reaction temperature; therefore, it tends to erroneously overestimate ignition parameters for near-limit fuel mixtures. This study has found that reaction heat release rate criterion can be used at all equivalence ratios and faithfully produces ignition parameter trends for fuel mixture reaction schemes of varying simplifications. Reaction heat release rate is a valid ignition criterion because the location of peaks in reaction released heat at varying times corresponds to flame front location, which is its physical counterpart.